Those who want to make practical improvements quickly with those limited funds available (from developing country governments, foreign aid, charity, etc.) need to make effective use of those funds. I don't think it is a stretch to say it is a moral obligation to make sure those funds are put to good use.
Doing RCTs is quite key to identifying the most effective approaches whether the goal is lives saved/$, incremental years of education/$, malaria cases reduced/$, etc. With that data, you can direct funds to the most efficient cause in any given area.
Duflo & Banerjee are quite modest about any judgement on whether the focus should be on improving quantity or quality of life and how one should measure quality of life. Their books are quite clear that one's one view of preferences doesn't necessarily line up with those who you are trying to help.
And one last point, yes, of course, their work would go through ethics review panels. Basically anything with human subjects does and their work would obviously qualify.
But that aside, what I find disturbing is the economic couching of basic human questions: do you need economic long-term effects that can be proven to provide deworming to poor children? Is that what we have arrived at - wellbeing is not even a concern. A fictional economic greater good is the measure of success, the health and comfort of poor people is not?
I'd say there is really a need for soul-searching among economists - to rethink why capitalism has brought so much property but also leaves so many people in poverty, and why it has taken such radical forms that in the richest country on earth thousands starve and tens of thousands die of treatable medical issues - and millions more in a global view.